Insufficient Material

I was playing 10 Minute Chess today and I had a king and my opponent had a king, rook, and pawn and the time ran out for my opponent. Surprisingly enough the game was drawn because of insufficient material. Why is this? Thanks.

Another thread on this? ...Okay, I'll explain: There is no logical reason for your opponent to win, as he flagged, but there was no logical reason for you to win, as there is no way for you to win on the board with no material. Thus, a draw.

Help us finish translating:

We are working hard to make Chess.com available in over 70 languages. Check back over the year as we develop the technology to add more, and we will try our best to notify you when your language is ready for translating!